Migration to pydantic v2

[alyssadai]

The release of Pydantic V2 introduced several breaking changes in the code due to name changes of multiple methods, removed or deprecated types/methods/objects, and broader changes to the logic of fields, validators, + more.

The docs for V2 have not quite caught up to the changes yet, but there is a comprehensive migration guide 🎉
https://docs.pydantic.dev/dev-v2/migration/ and pretty detailed PydanticUserErrors

Related are:
#179

TODO:

• investigate needed refactor for moving to pydantic 2
• refactor to enable pydantic 2 and migrate

[alyssadai]

Any thoughts @surchs?

I've started making some of the necessary changes (based on currently failing tests) in a branch and think the migration shouldn't require any major rewrites on our end, but some of the updates related to deprecated methods would probably benefit from a closer look as they involve a bit of extra code to preserve existing behavior.

[surchs]

Bumping this up since my ill advised late night commit (1d4cb52) to main has made this an actual blocker.

[alyssadai]

Will pin pydantic version for now. Taking this issue off of backlog in favour of #184.

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